Power supply unit, more specifically battery charger for electric vehicles and the like

ABSTRACT

A clocked current supply apparatus for connection to the network with one or several cables has at least one input rectifier, at least one regulator for generating a sequence of current pulses, at least one adapter network for separately transmitting potential and current pulses and a pair of output terminals for each adapter network to which a voltage-controlling element (accumulator, capacitor) is connected. The adapter network (AN) consists of an adapter transformer (TR) and several blocking diodes (DL,DE) that connect the output terminals (KA+, KA-) to the secondary winding system of the adapter transformer (TR). In addition, a regulator that consists of at least one choking coil (L), at least one pair of electronic switches (ES1,ES2) driven by a controller (STG) and one voltage limiter (BGU) is arranged between the rectifier (GR) and the adapter network (AN). The regulator generates a sequence of current pulses from the rectified mains voltage or from a direct voltage preferably connected to the apparatus by switches (SW). The energy of the current pulses flows through the adapter network (AN) to the output.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage Application under 35 U.S.C.§371, of PCT International Patent Application Number PCT/DE95/00985,(published as International Publication Number WO 96/03791), filed Jul.20, 1995, that designated the United States.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a switched-mode power supply unit withsingle-phase or multi-phase mains connection for the generation ofisolated d.c. voltages, and more specifically for charging a singlebattery or battery strings. The invention in particular relates to abattery charger for electric vehicles or the like.

2. Description of the Related Art

In general, power supply units, especially those of high power ratings,are expected to load the mains with active power only. To keep chargingtimes of high-capacity batteries short it is aimed at fully using themaximum power supplied by the mains, whereby the waveform of the linevoltage must not unsuitably be distorted by line current interference.Moreover, batteries that consist of a string of series-connectedelectrochemical cells shall, in general, have a long service life.Premature damages and early failures of single battery blocks due to, inpractice, unavoidable differences in capacities of the battery blockscan be avoided by obtaining, in each charging procedure, identicalvoltages for the individual battery blocks. During a discharging cyclethe differences in capacity between the single battery blocks can becompensated by corresponding permanent charge equalisation performed bythe charger.

It is well-known that, because of their excellent efficiency,switched-mode power supply units are used for charging batteries.According to the best known working principle the line voltage isconverted into a smoothed d.c. voltage, using diodes and capacitors,from which electronic switches generate voltage pulses of frequenciesranging between 10 kHz and 100 kHz. These voltage pulses are thenapplied to the primary winding of a suitable transformer and, thereby,generate an impressed a.c. voltage in the secondary winding; saidvoltage being shaped to the desired output voltage by means of arectifier and filter circuit. Then, this output voltage is conductedthrough a control unit in such a way that the desired charging currentdevelops (cp. U. Tietze, Ch. Schenk: "Halbleiterschaltungstechnik",Springer-Verlag, 5th Edition, 1980, pages 395 ff.).

Moreover, it is well-known that, in units with single-phase mainsconnections, the line current may be conducted in a sinusoidal waveformif the rectified line voltage is further treated by a boost converterinstalled downstream the rectifier, a combination often called step-upconverter (cp. U. Tietze, Ch. Schenk: "Halbleiterschaltungstechnik",Springer-Verlag, 5th Edition, 1980, pages 395, as well as M. Herfurth:"Aktives Oberschwingungs-filter mit konstanter Betriebsfrequenz und 600W Ausgangsleistung", Semi-Conductor Application Report of SIEMENS, PrintReference PD 22 9002). In such a circuit, the rectified line currenteither flows through an inductor, which takes on magnetic energy, and anelectronic switch, or through the inductor, the isolating diode and avoltage-determining element (capacitor, battery), energy beingtransmitted from the inductor to the voltage-determining element. TheON/OFF times of the electronic switch are controlled depending on theline voltage waveform so that a line current of an almost sinusoidalshape is developing. Here, the line current amplitude results from therequired power to be converted. A corresponding control method is knownfrom the application instructions for special integrated circuits (e.g.Claudio de Sa e Silva: Power Factor Correction with the UC 3854,Application Paper of UNITRODE).

With regard to batteries consisting of a string of series-connectedbattery blocks it is known that, due to always existing differences incapacity of the single battery blocks, the check for the sum of allblock voltages to determine the charging level leads to differentcharging levels of the individual battery blocks. Single battery blocksmay get damaged because of unnoticed exhaustive discharge or overcharge.DE 39 40 928 C1 describes how to prevent such effects. Accordingly,using the known principle of flyback converters, a certain energyquantity per time unit is withdrawn from the battery and, subsequently,supplied to the battery block with the lowest voltage. In this way, theaverage discharging current of a low-charged battery block is smallerthan that of battery blocks with higher charge levels.

A major disadvantage of switched-mode power supply units with rectifiedvoltages smoothed by capacitors is the pulse-shaped waveform of the linecurrents they generate. With consideration of the fuse elementsprescribed for mains supply lines, in practice, power conversioncapacities approximately half as big as the maximum power available fromthe mains on sinusoidal currents are obtained. Moreover, pulse-shapedline currents produce interference voltages across line impedances thatmay disturb other consumers connected to the same mains.

The application of the so-called step-up converter principle has thedisadvantage of allowing to generate only one output voltage that mustalways be higher than the amplitude value of the line voltage. Anelectrical isolation between line voltage and output voltage does notexist. Regarding a.c. mains with an effective voltage of 230 volts, theamplitude of the line voltage is 325 volts. So, an isolated outputvoltage which is lower than the amplitude value of the line voltage canonly be generated if the input voltage of the step-up converter isreduced by a line transformer. Usually, a power supply unit has toprovide for several output voltages ranging between about 5 and 100volts. It is very expensive to provide for a separate step-up converterincluding a line transformer for each output voltage to be generated.The rated voltage of traction batteries normally is less than 250 volts.Chargers for traction batteries shall have high charging capacities. Inmost cases an electric isolation is also required. Hence, a chargeraccording to the step-up converter principle has to be fitted with aline transformer which, however, increases the weight and the volume ofthe charger unit considerably.

According to one embodiment of DE 39 40 928 C1 charge equalising isachieved by means of one single storage transformer having a separatesecondary winding for each battery block. The disadvantage of thisconfiguration is that, to obtain the desired effect, the magneticcoupling among the individual secondary windings as well as the couplingof each secondary winding and the primary winding must be the same. Therealisation of such transformers gets the more difficult, the morebattery blocks have to be monitored. Moreover, the number of batteryblocks to be monitored is given by the number of existing secondarywindings. Another embodiment assigns each battery block its own flybackconverter. In this case, however, the expenditure in component partsboth for the power electronics and signal processing is high. Thecircuitry of DE 39 40 928 C1 only relate to charge equalising amongbattery blocks; charging of a battery itself is not provided for.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide for a power supplyunit that does only draw active power from a single- or multi-phasemains avoiding undesired current harmonics, one that does not need anyline transformer, and which is capable of generating one or severalisolated output voltages, and, when being used as a battery charger,ensures continuous charge equalising between the single blocks of thebattery both during charging and discharging cycles.

The general advantage of the configuration of the present invention isthat the voltage adjusting transformers ensure an insulation betweeneach output and the mains. So, it is either only one consumer or severalconsumers being galvanically not interconnected or severalseries-connected consumers that can be supplied. The output voltages arematched in a simple way by selecting the turn ratios of the voltageadjusting transformers. A line transformer is not necessary. Due to thehigh pulse frequency the volume of the voltage adjusting transformerscan be kept small resulting in small converter weight and size. Asuitable ON/OFF timing of the electronic switches allows to conduct theline current in a sinusoidal waveform and, hereby, enables high power tobe drawn from the mains. In particular, it is possible to fully use thepower available at household sockets, that is approx. 3.3 kW. The linecurrent has no low-frequency harmonics producing distortions of the linevoltages. Due to its modular configuration the power supply unitaccording to the present invention can be configured for differentsupply tasks at any time. In particular, battery charging requiresseveral identical output circuits that are to be dimensioned for thecharging power of one battery block each. Therefore, it is normallypossible to do with easily available and reasonably priced componentparts. The use of several identical components enables rationalisedmanufacturing of the power supply.

A configuration according to the present invention may equally be usedfor generating d.c. voltages, charging battery blocks, and chargeequalising among several battery blocks. To generate d.c. voltages theoutput terminals are connected to capacitors as voltage determiningelements. One single output voltage is measured and corrected to apreselected setpoint via a voltage control that is superimposed to theinductor current control. Since energy is always supplied to the mostloaded output, or outputs resp., the remaining not measured outputvoltages are indirectly controlled, too--similarly to a fly-backconverter system. They mainly develop according to the turn ratios ofthe voltage adjusting transformers. To charge a battery, each batteryblock is directly connected to the output terminals. A capacitor may, inaddition, be connected in parallel to compensate the inner inductance ofthe battery block. During the initial charging phase, the batteryblocks--starting with the block having the lowest voltage--aresuccessively brought up to the same voltage. In the second phase, thebattery blocks, now having identical voltages, are completely charged upto the final charging voltage without overcharging single batteryblocks. In this way, it is made sure that each battery block obtains themaximum charge corresponding to its capacity. Harmful overcharging isavoided thus prolonging the service life of a battery. Batterymaintenance by means of regular measurements of the battery voltages andwell-aimed charging or discharging of single battery blocks is notneeded. The permitted charging power of a battery block can be adjustedin a simple way if the control unit detects the number of battery blockswith the lowest voltage and presets for the converter a charging powercorresponding to the determined number multiplied by the permittedmaximum charging power of one single battery block. Because of theparallel connection of the output circuits at the converter output, thedevice is, at any time, capable of being matched to the number ofbattery blocks. During discharging cycles, the configuration accordingto the present invention enables low-capacity battery blocks to besupported advantageously. When the line voltage is not applied theswitches SW are closed (cp. FIG. 1c) and the converter can be suppliedfrom the battery itself. The energy withdrawn from the battery reachesthe weakest battery block or blocks, respectively. Thereby, on the timeaverage, a discharging current is drawn from the single battery blockscorresponding to their capacity, and it is made sure that, at any time,the charge levels of all battery blocks are equal.

Due to the unavoidable leakage inductances of the voltage adjustingtransformers it takes a certain time until the current pulses suppliedby the converter flow through the primary windings of the voltageadjusting transformers completely. Therefore, the voltage adjustingtransformers have to be designed with as low leakage inductances aspossible. As long as the current transfer is not completed, thedifference between the current pulse supplied by the converter and thecurrent flowing to the primary windings is taken on by a voltagelimiter. The energy transmitted to the voltage limiter may, totally orpartially, be recuperated to improve the efficiency by suitablydesigning said voltage limiter.

In another embodiment of the present invention (cp. FIG. 3), theinductor is connected to the line rectifier and to a bridge assembly offour electronic switches the a.c. connections of which lead to theparallel connected primary windings of the voltage adjustingtransformers. In principle, this circuitry has the same features as thebasic circuit shown in FIGS. 1a/1b/1c and has the additional advantageof enabling the secondary windings and isolating diodes to be, on thetime average, loaded equally, which is favourably influencing thedimensioning of both the isolating diodes and the wire cross-sectionareas of the primary and secondary windings. In principle, there is thechoice between a demagnetisation of the transformer cores during thecharging of the inductor and a magnetic reversal during the transmissionof a current pulse. If the transformer cores have been demagnetised atthe beginning of the transmission of a current pulse the time which, dueto the leakage inductances of the output circuits, is needed to fullytransmit the current pulse to the output circuits is shorter, and theload on the voltage limiter is smaller than if a magnetic reversal ofthe transformer cores occurs during the transmission of a current pulse.The advantage of magnetic reversal, however, is that the transformercores can be magnetised according to the so-called push-pull operationwith varying signs, thus providing for a greater induction range. Inthis case, less core material is needed. Components only serving fordemagnetising the transformers are not needed in the circuit accordingto FIG. 3.

Another embodiment of the present invention (cp. FIG. 4) is fitted withvoltage adjusting transformers having a primary winding with a centraltap. To avoid undesired circulating currents between the primarywindings of several output circuits diodes DP forming additionalcomponents of the output circuits can be connected in series with eachwinding half. Each output circuit has three input terminals KX, KY, KZat which it is connected in parallel to all the other output circuits.The sequence of current pulses generated by the converter is fed to thecommon connecting point of all central taps KX. Terminals KY and KZleading to the winding ends via diodes are connected to an electronicswitch each. This circuit, in principle, has the same features as thecircuit depicted in FIG. 3, but can do with only three electronicswitches and, to simplify the triggering of the switches, all theseelectronic switches can be connected to a common reference potential.Circulating currents between the voltage adjusting transformers may beprevented, which is advantageous for units having many or spatiallyseparated output circuits.

Another embodiment of the present invention (cp. FIG. 5) has twoinductors L1, L2 each being connected to the rectifier GR on the onehand and to a terminal of the parallel connected voltage adjustingtransformers as well as to an electronic switch on the other. As long asan electronic switch is conducting, the inductor assigned to it is beingcharged. To transmit a current pulse to the output circuits oneelectronic switch has to be switched off and the other one must beconducting. Both electronic switches are triggered displaced by 180°related to the switching period. This results in two sequences ofcurrent pulses with different sign that are applied to the primarywindings of the voltage adjusting transformers, thus resulting inpush-pull operation. This circuit has an advantage over theabove-described configurations acc. to FIGS. 1a/1b/1c and FIG. 3 as,with identical inductance values of the inductors and identical pulsefrequencies of the electronic switches, the division of the power flowonto two inductors and two switches with displaced triggering results ina reduction of the distortion ripple of the line current, thus allowingsmaller filter elements to suppress line current components with pulsefrequency. The use of two inductors with half the current load offersdesign advantages over the application of one inductor having to bedesigned for the entire device capacity. The push-pull operation allowssmall transformer cores. Moreover, one can do with two electronicswitches that are connected to one and the same reference potential,which facilitates the triggering of the electronic switches.

Another embodiment of the present invention (cp. FIG. 6) has two basiccircuits connected in parallel at the output terminals of the rectifiereach of them supplying energy to the voltage adjusting transformers viaone of their two independent primary windings. To avoid circulatingcurrents between the voltage adjusting transformers diodes DP can beconnected as components of the respective output circuits to eachprimary winding. The two basic circuits are operated with a displacementof 180° related to the switching period. This circuit type has all theadvantages indicated for the circuits according to FIGS. 1a/1b/1c, FIG.3, and FIG. 5. All the electronic switches are connected to the samereference potential, which simplifies their triggering. The suppressionof circulating currents by diodes connected in series with the primarywindings of the voltage adjusting transformers is advantageous for unitshaving many or spatially separated output circuits.

For a three-phase mains connection the objective of this invention isreached by connecting two of the above-described circuits in parallel atthe output terminals, by connecting one a.c. terminal of each of the tworectifiers to a line terminal, by connecting the two remaining terminalsof the rectifiers to the remaining line terminal, and by conducting twoline currents by means of two independent control units in such a waythat each of them is in phase with the line to line voltage across thea.c. terminals of the assigned rectifier (cp. FIG. 7).

The combination of two identical units simplifies the manufacture ofdevices with three-phase mains connections. In combination withstandardised output circuits the power supply unit can easily be matchedto varying requirements as regards number and value of the outputvoltages as well as power rating. Especially for units with high powerrating, the splitting-up of the power into weaker components enablingthe use of elements which are more easily to acquire or less expensivemay be advantageous. As the neutral point of the mains is not connectedthe sinusoidal conduct of two line currents results in a sinusoidalwaveform in the third phase as well. Hence, the mains is only loadedwith active power.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1a is a block diagram of the basic circuit to generate an outputd.c. voltage;

FIG. 1b is a block diagram of the basic circuit to charge a batteryblock;

FIG. 1c is a block diagram of the basic circuit to charge a batteryconsisting of two series-connected battery blocks;

FIG. 2 depicts an embodiment of the power section of the basic circuit;

FIG. 3 is a block diagram of a circuit having an inductor and fourelectronic switches in bridge configuration;

FIG. 4 is a block diagram of a circuit having an inductor and threeelectronic switches;

FIG. 5 is a block diagram of a circuit having two inductors and twoelectronic switches;

FIG. 6 is a block diagram of a circuit having two inductors and fourelectronic switches;

FIG. 7 is a block diagram of a circuit with three-phase mainsconnection;

FIG. 8 depicts another embodiment of an output circuit.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings representembodiments of the present invention, the drawings are not necessarilyto scale and certain features may be exaggerated in order to betterillustrate and explain the present invention. The exemplification setout herein illustrates embodiments of the invention, in several forms,and such exemplifications are not to be construed as limiting the scopeof the invention in any manner.

DESCRIPTION OF THE PRESENT INVENTION

The embodiments disclosed below are not intended to be exhaustive orlimit the invention to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may utilize their teachings.

In the basic circuit to generate an output voltage acc. to FIG. 1a, theline voltage is applied to the line terminals K˜ and rectified by arectifier GR consisting of four diodes. Together with the two electronicswitches ES1, ES2 (e.g. IGB Transistors) being alternatively switched ONand OFF within the kHz range and a voltage limiter BGU, an inductor Lforms a converter with switched output. The converter is connected tothe terminals KX and KY of an output circuit AN. The latter consists ofa voltage adjusting transformer TR and isolating diodes DL ("changingdiode") and DE ("demagnetising diode") which prevent a reverse currentto the output circuit AN. The primary winding of the voltage adjustingtransformer TR is connected to the terminals KX and KY. A capacitor C asa voltage determining element and a consumer R are connected across theoutput terminals of the output circuit AN. Capacitor C buffers theenergy supplied to the consumer R via output circuit AN. The triggersignals for the electronic switches ES1, ES2 are generated by a controlunit STG. When the electronic switch ES1 is conducting, the rectifiedline voltage is applied to the inductor L which, while this is beingdone, takes on magnetic energy. In this time, electronic switch ES2 isblocking so that the magnetic energy ES2 is blocking so that themagnetic energy that had been stored in the core of the voltageadjusting transformer TR during the preceding switching period istransmitted to the output. During demagnetisation, a current is flowingthrough isolating diode DE, terminal KA+ to the capacitor C as well asto the consumer R and from there via terminal KA- back to the centraltap of the secondary winding. Due to the voltage at the capacitor C itdecreases linearly as to time. The interval in which the electronicswitch ES1 conducts and the electronic switch ES2 isolates, preferably,is longer than or equally long as half the switching period and isadjusted in dependence on the desired waveform of the line current.Subsequently, the electronic switch ES1 is kept off and the electronicswitch ES2 kept on up to the end of the switching period. Then, theinductor L impresses a current pulse which flows across the primarywinding of the voltage adjusting transformer TR. After an initial delaytime which is dependent on the value of the leakage inductances of thevoltage adjusting transformer TR, it is split up into one portion thatserves for magnetising the transformer TR and another portion thatcorresponds to the current induced in the secondary winding. This isflowing via isolating diode DL, terminal KA+ to capacitor C and consumerR and from there via terminal KA- to the central tap of the secondarywinding. As long as a current is flowing through isolating diode DL,part of the energy stored in the inductor L is transmitted to thecapacitor C and the consumer R, the voltage at the primary winding andat electronic switch ES1 being multiplied by the turn-ratio of theprimary and secondary winding. By repeatedly switching on and off theelectronic switches ES1 and ES2 a sequence of current pulses is appliedto the parallel connection of the capacitor C and the consumer R. Whentheir energy, on the time average, is identical to the energy dissipatedby the consumer R, the capacitor voltage is almost constant. The latteris measured by an isolating voltage measuring unit MGU and adjusted by avoltage controller RGL. The voltage controller RGL presets the linecurrent amplitude necessary to maintain the capacitor voltage (which isidentical to preset the power to be converted) for the control unit STGin dependence on the measured capacitor voltage and the capacitorvoltage setpoint preset by a setpoint device SGU. The control unit STG,using the current measuring unit MGI, measures the output current of therectifier GR which corresponds to the current flowing across theinductor L and determines the ON and OFF signals for the electronicswitches ES1, ES2 in such a way that the current through the inductor Lis analogue to the absolute value of a sinusoidal function. Then, theline current is sinusoidal. The electronic switch ES1 being OFF and theelectronic switch ES2 being ON, the current in the secondary winding,and likewise the corresponding current portion in the primary winding,due to the unavoidable leakage inductances of the voltage adjustingtransformer TR, does not increase steplike but like a ramp. Thedifference between the current pulse impressed by the inductor L and thecurrent through the primary winding is taken on by a voltage limiterBGU. The smaller the leakage inductances of the voltage adjustingtransformer TR, the faster the increase of the current in the secondarywinding and the less the energy to be taken on by the voltage limiterBGU. When the unit transmits very little power, the current pulseimpressed by the inductor L may be shorter than the ON period of theelectronic switch ES2 determined by the control unit STG. In this case,an undesired additional magnetising current driven by the rectified linevoltage may develop across the primary winding of the voltage adjustingtransformer TR. This can be avoided by prematurely switching off theelectronic switch ES2. A criterion for switching off is a rapidlydecreasing primary voltage at the voltage adjusting transformers TRafter a current pulse has been transmitted. To prevent an undesiredmagnetising current when converting extremely low power, it is generallysufficient to switch off all electronic switches after a voltagebreakdown across the primary windings. This also applies to all circuitsdescribed hereafter.

FIG. 1b shows a block diagram of the basic circuit for charging abattery. The battery AK is connected to the output terminals KA+ and KA-of the output circuit AN. As, in comparison with capacitors, batterieshave high capacities the voltage at the battery AK only changes veryslowly. For the control of the charging procedure it is thereforesufficient to have the battery voltage checked by an isolating voltagemeasuring unit and evaluated by a function block FKT. The latter presetsthe charging power for the control unit STG. As a rule, it is themaximum permitted power from the start of the charging procedure forsome time and decreases continuously when approaching the end-of-chargevoltage. Control of the electronic switches ES1, ES2 and energytransmission are done as described for FIG. 1a.

FIG. 1c depicts the basic circuit for charging battery strings and forcharge equalising among several battery blocks. As each battery block AKhas an output circuit AN with an isolation ensured by the voltageadjusting transformers TR it is of no importance whether individualbattery blocks AK or series-connected battery blocks AK or a combinationof single and series-connected battery blocks AK shall be charged. Thesame applies to charge equalising. Usually, batteries are composed of astring of identical series connected battery blocks AK, which justifiesthe use of identical output circuits AN. To simplify matters, FIG. 1cdepicts a battery B consisting of two series-connected battery blocksAK. Each battery block AK is connected to an output circuit consistingof a voltage adjusting transformer TR and the isolating diodes DL andDE. The primary windings of the voltage adjusting transformers TR areconnected in parallel at the terminals KX, KY and to the converteroutput. To charge the battery blocks AK the line voltage is applied tothe line terminals K˜ while the switches SW are in the OPEN position. Toachieve charge equalising during the discharge of battery B or duringrecuperation, the line terminals K˜ are OPEN and the switches SW closed.In this case, the circuit is supplied from battery B. For batterycharging as well as charge equalising, the converter composed of theinductor L, the electronic switches ES1, ES2, and the voltage limiterBGU is switched as described for FIG. 1a. During the demagnetisingphase, each voltage adjusting transformer TR shortly generates a currentthat flows to the battery block AK being connected to the respectiveoutput circuit. If the output circuits AN are identical, the currentpulse impressed by the inductor L is, at the beginning, a magnetisingcurrent that evenly split up on each voltage adjusting transformer TR.In the output circuit AN with the battery block AK having the lowervoltage, the isolating diode DL gets conductive first. The voltage ofthis battery block AK, then, determines the primary voltage of allvoltage adjusting transformers TR; as a consequence, the isolating diodeDL of the output circuit AN that is connected to the battery block AKwith the higher voltage stays isolated. Thus, energy from the inductor Lonly gets to the battery block AK with the lower voltage via therespective voltage adjusting transformer TR and the respective isolatingdiode DL. As long as, at one output circuit AN, the energy of thecurrents generated by demagnetisation is lower than the one transmittedwhile the electronic switch ES1 is OFF, it is, on the time average, thebattery block with the lower voltage that is mainly supplied withenergy. This condition can be met by suitably dimensioning the voltageadjusting transformers TR and by control measures. If the two batteryblock voltages are identical, the two isolating diodes DL are conductiveat the same time. Then, if the output circuits AN are equal, identicalenergy portions flow from the inductor L to the battery blocks AK. If aconsumer is connected to battery terminals K+ and K- and no line voltageis applied, the voltage at the weaker battery block AK decreases fasterthan that at the stronger battery block AK. If the converter is thensupplied from the battery B through the switches SW, the energy theconverter is taking from the battery B automatically reaches the batteryblock AK with the lowest voltage and, thus, reduces, on the timeaverage, its discharge current while the discharge current of thebattery block AK with the higher voltage increases. When battery B issupplied with energy through battery connection terminals K+ and K-(recuperation), the voltage at the low-capacity battery block AKincreases faster than that at the high-capacity battery block AK. Inthis case, the energy the converter draws from the battery Bautomatically reaches the high-capacity battery block AK. Thelow-capacity battery block AK, on the time average, takes on less energythan the high-capacity block. If, during discharge of battery B or at arecuperation, both voltages are identical, charge equalising is notneeded and the circuit is switched off. Output circuits AN aredimensioned for the maximum charging power of a single battery block AK.In order not to overload the output circuits AN the converter only mustconvert as much energy per time unit as is corresponding to the numberof battery blocks AK having the lowest voltage. To determine this numbera control element ZMI which evaluates the isolating voltage measuringunits MGU is needed. The output signal of the control element ZMI actson a limiter BGR. It reduces the power to be transferred, which afunction block FKT previously derived from the battery voltage, to thepermitted value. The total battery voltage is summed from all batteryblock voltages by a functional block SUM. To prevent undesiredcirculating currents between the primary windings diodes may, withoutany function losses, be connected in series to the primary windings asfurther components of the output circuits (cp. FIG. 2).

FIG. 2 shows an embodiment of the basic circuit shown in FIG. 1c whichfeatures series diodes DP connected to the primary windings to suppressundesired circulating currents between the voltage adjustingtransformers TR. The current measuring unit MGI is formed by a singleresistor. To prevent the inductor current components of higher frequencycaused by the switched mode of the controls from flowing across thepower cables a filter capacitor CF is integrated in parallel to therectifier GR. When the electronic switch ES1 is switched off, theunavoidable leakage inductances of the voltage adjusting transformers TRdelay the transfer of the current pulses from the inductor L to thevoltage adjusting transformers TR. During this delay time, the voltagelimiter BGU takes on the differential current. It flows through the mainBGU components, i.e. diode D3 and capacitor CU. The differentialcurrents gradually charge the capacitor CU so that a discharge circuitis needed to ensure a given voltage at the capacitor CU. The latterconsists either of a discharge resistor RU allowing to recuperate partof the energy buffered at the rectifier GR or of an electronic switchES3 or of a combination of the two. The use of the electronic switch ES3allows to recuperate the entire energy stored on capacitor CU. Togetherwith the electronic switch ES2, it will always be switched on when theinductor L impresses a current pulse. As long as the diode D3 isconducting, the capacitor CU is being charged (proceeding from a presetminimum voltage) and electronic switch ES3 is bypassed. As long as thediode D3 is blocking, the capacitor CU can discharge via the electronicswitch ES3 and the primary windings of the output circuits AN, theenergy from the capacitor being supplied to the battery block with thelowest voltage. At that moment the voltage at capacitor CU decreasesbelow the preset minimum voltage, the electronic switch ES3 is switchedoff. The diodes D1, D4 ensure a current path for the demagnetisation ofthe primary leakage inductances of the voltage adjusting transformers TRwhen the electronic switch ES2 is switched off. In practice, thesediodes are usually not needed since the energy stored in the primaryleakage inductances of the voltage adjusting transformers TR is soinsignificant that it is taken on by the winding capacitances. Tosimplify matters FIG. 2 and the following figures only outline thecontrol unit. The components to determine the power to be transmittedknown from FIG. 1c are omitted.

The embodiment shown in block diagram FIG. 3 incorporates a converterwith a bridge assembly of four electronic switches ES1, ES2, ES3, andES4. This allows to preset the current flow direction through theprimary windings and to influence the operating mode of the voltageadjusting transformers TR. The timing of the electronic switches is doneanalogue to the explanations of FIG. 1a, the only difference being thatit is always at least two electronic switches that are conducting. Ifthe voltage adjusting transformers TR shall be demagnetised while theinductor L is being charged, either electronic switches ES1 and ES3 haveto be switched on and electronic switches ES2 and ES4 switched off orvice versa. If all electronic switches only allow one direction of thecurrent flow and can take on isolating voltages in both directions, thenone line to the output circuits AN connected in parallel at theterminals KX and KY is interrupted so that the magnetising currentspreviously flowing into the primary windings are commutating into thesecondary windings and the magnetic energy stored in the cores ofvoltage adjusting transformers TR reaches battery blocks AK. Uponcompletion of the charging of the inductor L, a current pulse flowing toterminals KX is generated by switching on electronic switches ES1 andES4 and switching off the other two switches. When the electronicswitches ES2 and ES3 are conducting and the other two are notconducting, a current pulse flowing to terminals KY is generated. If thesign of the current pulses through the primary windings is changed foreach switching period, the two halves of the secondary winding of avoltage adjusting transformer and diodes DL are, on the time average,loaded uniformly. This is expressed by equally marking the isolatingdiodes with DL. The push-pull operation of the voltage adjustingtransformers TR is characterised by the fact that the magnetisation ofthe transformer cores only changes during the transfer of a currentpulse. Otherwise, the magnetisation of the voltage adjustingtransformers TR remains almost constant. This is achieved byshort-circuiting all primary windings during the charging of theinductor L. In order to enable short-circuit currents with differentsigns in the primary windings all the electronic switches must, at anytime, be capable of conducting a current of any sign. This may always beachieved by means of an inverse-conducting diode connected parallel tothe respective electronic switch. In the push-pull operation mode doublethe induction range may be utilised as compared to the demagnetisingoperation mode. This allows to use smaller transformer cores.Alternatively, the voltage limiter BGU may also be connected in parallelto the terminals KX and KY if it is capable of limiting voltages withvarying signs.

The circuit according to FIG. 4 includes a converter that, as comparedto the basic circuit, has another output line fitted with the electronicswitch ES3. The primary windings of the voltage adjusting transformersTR are provided with a central tap each that conducts to terminal KX. Toavoid circulating currents between the voltage adjusting transformers TRthe ends of the primary windings may be connected with a series diodeeach to the terminals KY and KZ of the output circuits AN. At theterminals KX, KY, and KZ, all output circuits are connected in parallel.The inductor L is charged by switching on the electronic switch ES1. Thecurrent pulse impressed by the inductor L, while the electronic switchES1 is switched off, flows to the terminals KX and from there eitheracross one half of the primary windings to the terminals KY and theelectronic switch ES2 (with ES3 isolating) or across the other half ofthe primary windings, the terminals KZ, and the electronic switch ES3(with ES2 isolating), while the signs of the magnetisation of eachtransformer core are varying. At the electronic switch that is notinvolved in the current flow, the magnetic coupling between the twohalves of the individual primary windings generates a maximum isolatingvoltage double the voltage adjusted at the voltage limiter BGU. If thecores of the voltage adjusting transformers TR shall be demagnetisedduring the ON-period of the electronic switch ES1, the electronicswitches ES2 and ES3 remain OFF for this time. If one does without theseries diodes DP, the electronic switches ES2, ES3 must only permit onecurrent flow, direction and must be capable of taking on isolatingvoltages of different signs. If the electronic switch ES1 always allowsan inverse current the above-described push-pull operation is achievedby switching on all the electronic switches while the inductor L ischarged.

According to the circuit shown in FIG. 5 the power to be converted issplit up on two converters. They consist of the electronic switch ES1,the inductor L1, and the voltage limiter BGU1, and of the electronicswitch ES2, the inductor L2, and the voltage limiter BGU2 respectively.Both converters are supplied with energy from rectifier GR or, ifswitches SW are closed, from battery B. The inductors L1, L2 are eachdimensioned for half the maximum power of the unit. When the electronicswitch ES1 is switched off and the electronic switch ES2 is conducting,the inductor L1 impresses a current pulse that flows to the terminals KXacross the primary windings, to the terminals KY of the output circuitsAN, and across the electronic switch ES2, while inductor L2 is beingcharged. When the electronic switch ES2 is switched off and theelectronic switch ES1 is conducting, the current pulse impressed by theinductor L2 flows in the inverse direction, while the inductor L1 isbeing charged. While all electronic switches are conducting, bothinductors L1, L2 are charged and the terminals KX and KY areshort-circuit. Only in very special cases (e.g. transmission ofextremely low power, fault conditions) it is reasonable to switch offboth electronic switches. If an identical ON/OFF time ratio is presetfor the electronic switches ES1, ES2 and the switching cycles aredisplaced by 180° during one switching period, a positive current pulse,a short circuit, a negative current pulse, and another short circuit aresuccessively applied to the output circuits AN connected in parallel atthe terminals KX and KY. The short-circuit phases only enable apush-pull operation. For this purpose, the two electronic switches, whenconducting, have to be capable of carrying a current of any sign. Tofulfil this condition the electronic switches can additionally be fittedwith inverse-conducting diodes D1 and D2. If the inductances of theinductors L1, L2 and the pulse frequency are adjusted to the same valuesas for the circuits according to FIGS. 1a/1b/1c to FIG. 4, the circuitacc. to FIG. 5, due to the displaced switching, leads to a morefavourable ripple spectrum of the line current, which reduces thenecessary filtering measures. Alternatively, it is possible, at a givenpermitted ripple of the line current, to adjust a lower inductance ofthe inductors L1, L2. As an alternative to the two voltage limitersBGU1, BGU2 a voltage limiter that is capable of limiting a voltage withvarying sign may be connected in parallel to the terminals KX and KY. Ifone of the two lines to the terminals KX and KY can be interrupted viaelectronic switches, partial demagnetisation can be performed asdescribed for the circuit according to FIG. 6.

The circuit according to FIG. 6 includes two converters with oneswitched output each. They consist of the electronic switches ES1, ES3,the inductor L1, and the voltage limiter BGU1, and the electronicswitches ES2, ES4, the inductor L2, and the voltage limiter BGU2 resp.,and are both supplied with energy from the mains through the rectifierGR or, if the switches SW are closed, from battery B. The voltageadjusting transformers TR of the output circuits AN have two independentprimary windings each, each winding being assigned to a converter. Aseries diode DP may be connected to each primary winding in order tosuppress circulating currents between the voltage adjusting transformersTR. When the electronic switches ES1 and ES4 are OFF and the electronicswitches ES2 and ES3 are ON, the inductor L1 impresses a current pulsethat is flowing to the terminals KX1 of all output circuits AN and thento terminals KY1 and the electronic switch ES3, the inductor L2 beingcharged simultaneously. When the electronic switches ES2 and ES3 are OFFand the electronic switches ES1 and ES4 are ON, the inductor L2impresses a current pulse that is flowing to the terminals KX2 of alloutput circuits AN and then to terminals KY2 and the electronic switchES4, the inductor L1 being charged simultaneously. When a current pulseis impressed, the energy reaches the battery blocks AK with minimumvoltage as described above. The two converters run with a displacementof 180° related to the switching period. If the charge period for aninductor is longer than the transfer period of a current pulse, theintervals in which one of the inductors impresses a current pulse willalways be followed by times in which both inductors are charged at thesame time; during this time, the switching state of the electronicswitches ES2 and ES4 determines whether the push-pull operation isachieved by a short circuit between the terminals KX1 and KY1, and KX2and KY2 resp., or by a partial demagnetisation of the transformer cores.If, in that time, the electronic switches ES2 and ES4 are conducting andthe electronic switches ES1 and ES2 allow an inverse current, thecurrents in the primary windings can continue flowing in short circuits.If, however, the electronic switches ES2 and ES4 are not conducting, thetransformer cores are partially demagnetised via the secondary windings;here, the electronic switches ES2 and ES4, doing without the seriesdiodes DP, must only allow one current direction and have to take onisolating voltages in both directions. Before a total demagnetisationwill take place, the displaced switching of the converter results in atransmission of another current pulse and, thus, in a magnetic reversalof the transformer cores starting from the magnetising state existing atthe end of the partial demagnetisation. The current pulses impressed bythe inductors L1 and L2 cause different signs of the magnetisation sothat all windings of one voltage adjusting transformer TR and theassigned isolating diodes DL are, on the time average, loaded equally.

FIG. 7 shows a block diagram of a device with a three-phase mainsconnection. It consists of two basic circuits according to FIG. 1b. Tosimplify matters the figure only shows one battery block AK that isconnected to the output terminals KA+ and KA- of each output circuit AN.To feed further battery blocks each basic circuit may have severaloutput circuits. The rectifiers GR are connected to the three-phasemains via three mains terminals K1˜, K2˜, K3˜, one mains terminal beingcommon to both rectifiers GR. In FIG. 7, this is the terminal K2˜. So,the two basic circuits are operating at line voltages that are displacedby 120°. The line currents flowing through the rectifiers GR areadjusted in phase to these line voltages by the control unit STG. If theneutral of the mains is not connected, all line currents will havesinusoidal waveforms. The amplitude of all line currents is preset bythe function block FKT in dependence on the voltage of the battery blockAK determined by means of the voltage measuring unit MGU. In general, asymmetric three-phase current system is developing if each basic circuittransmits the same power. As an alternative to the basic circuits eachof the configurations shown in FIGS. 3 to 6 may be applied.

FIG. 8 shows an output circuit AN that, compared to the output circuitsdescribed above, has a voltage adjusting transformer TR with only onesecondary winding and, at the output, a bridge assembly consisting oftwo isolating diodes DL ("charging diodes") and DE ("demagnetisingdiodes"). The converter and one battery block AK are connected to theterminals KX, KY, and KA+, KA- resp., of the output circuit as shown inFIG. 1b. To simplify matters FIG. 8a only depicts the components of theconverter that are necessary for the connection of the output circuitAN. Apart from the double voltage drop of the bridge connection theoutput circuit AN acc. to FIG. 8 is equivalent to the output circuits ANshown in FIGS. 1a/1b/1c. The circuits according to FIGS. 3 to 6 may alsobe fitted with output circuits AN acc. to FIG. 8, whereby, due to theuniform current loading, a differentiation between the single isolatingdiodes is not necessary.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

I claim:
 1. A timed power supply apparatus for one of a single-strandedand multiple-stranded mains connection, comprising:at least oneinputside rectifier; at least one active element for generating asequence of current pulses, said active element including at least onechoke coil, at least one pair of electronic switches, and a voltagelimitation effective only in transfer actions, said voltage limitationcoupled to said rectifier, said active element having switchesgenerating a series of current pulses from one of a rectified mainsvoltage and a direct voltage source cut in; at least two matchingnetworks for potential-separated transmission of the current pulses,said matching networks coupled to said voltage limitation, each of saidmatching networks including a pair of output terminals, each matchingnetwork including a matching transformer and a plurality of blockingdiodes connecting said output terminals to a secondary coil system ofsaid matching transformer, with primary coil systems of said matchingnetworks being wired in parallel with one another, said current pulsesof said active element flowing only to those outputs that carry thelowest voltage, and whose energy flows at equality of voltage on alloutputs at equal parts to all outputs due to different transformerreactions of voltages prevailing across said output terminals of saidmatching networks on the primary voltage of said matching transformers;a voltage-determining element connected to each one of said pair ofoutput terminals, said voltage-determining element being one of anaccumulator and a capacitor; and a controller, said controlleractivating said electronic switches, said controller generating controlcommands for said electronic switches in a way such that in mainsoperation a sinusoidal mains current flows while in direct-voltageoperation a smoothed current is drawn from the direct voltage source,and with the output to be transmitted being specified to said controllerat minimal voltage in contingence on a characteristic stored in afunction generator and on the number of output channels.
 2. The timedpower supply apparatus of claim 1 wherein said direct-voltage source cutin of said switches includes a series-wiring of at least twovoltage-determining elements connected to outputs of said matchingnetworks.
 3. The timed power supply apparatus of claim 1 furthercomprising a bridge circuit including four electronic switches whereinsaid choke coil is connected to said rectifier and said bridge circuit.4. The timed power supply apparatus of claim 1 wherein said primary coilof said matching transformers has a center tap and said active elementincludes three electronic switches.
 5. The timed power supply apparatusof claim 1 further comprising two choke coils, one of said choke coilsbeing connected to one pole of said rectifier and each of said chokecoils being connected to one of two leads of said primary coils of saidmatching transformers, said choke coils also being connected to a firstline of two electronic switches, and the second line of said twoelectronic switches extends to the other pole of said rectifier.
 6. Thetimed power supply apparatus of claim 5 wherein said matchingtransformers have two primary coils, each said primary coil connectingto one of said two choke coils and one of said electronic switches andallowing switching to the other pole of said rectifier via a secondelectronic switches.
 7. The timed power supply apparatus of claim 5wherein said plurality of diodes are wired in series with each leg of aprimary coil of one of said matching transformers.
 8. The timed powersupply apparatus of claim 5 further comprising two circuits including atleast one of said matching networks, one of said rectifiers, one of saidactive elements, and output side wiring in parallel, onealternating-current terminal of each of said two rectifiers connects toone leg of a tri-phase voltage system, the other terminals of said tworectifiers connect to the third leg of the tri-phase voltage system, andthe mains currents of said rectifiers are managed by two of saidcontrollers in contingence on the mains voltages prevailing across saidrectifiers, that said rectifiers are in phase with the voltages carriedon the mains.